1. Field of the Invention
The present invention relates to a method of deriving safe separation distance of a missile based on time and acceleration, and more particularly to adjustments to this time for arriving at a safe separation distance for arming an electronic safe and arm in a missile.
2. Discussion of Related Art
Previously disclosed and known methods of deriving safe separation distance of a missile include using an escapement controlled mass displacement integration technique, or to double integrate an output signal of an accelerometer. These methods incorporate the use of a mechanical accelerometer for producing a voltage proportional to the acceleration of the missile used in combination with an analog circuit having operational amplifier integrators. Recently, micro machined accelerometers have been used together with analog to digital converters or pulse-train output signals. These signals are digitally double integrated in gate array ASICs or microcomputers.
Publications in physics and mechanical engineering texts provide a general discussion of Newtonian Mechanics and may include concepts for integrating acceleration to derive velocity and distance of a missile or a similar object. Publications and other reports disclose missile applications using double integration methods. Another source for information regarding safe separation of a missile is critical design review presentations and Army Fuze Safety Review Board presentations.
While the above described method functions adequately, it has a few drawbacks. The major drawback is that for all known applications where safe separation distance is derived, only double integration methods are used. In these applications, none of the descriptions mention the concept of measuring time to actual safe separation distance or the adjustment of this time for deriving a safe separation distance.
Furthermore, the integration method of deriving distance is complex both in terms of the quantity of hardware required, and the complexity of logic required in an ASIC or the complexity of algorithms required in a micro-computer. Both the digital ASIC and the microcomputer processing of the double integration method provide numerous categories in which errors can occur due to time delays during sampling and data processing.
Other issues in the application of the double integration method in calculating the safe separation distance include response to malfunctions of the acceleration sensor, processing circuits, guidance system and other missile functions. Although it is relatively easy to detect a full scale failure induced response, it is difficult to detect other significant deviations from a valid acceleration and time profile. A malfunction of any or all of the above responses could result in premature derivation of safe separation distance.
One solution in reducing the effects of these types of malfunction is to provide frequent monitoring of the acceleration profile during missile flight. To incorporate this type of monitoring using the double integration method cannot be effectively achieved. Frequent monitoring of the acceleration profile or profiles of the missile with the integration method would add considerable complexity. The analog and ASIC digital circuits disclosed in the prior art would be complex, and a micro-computer based system requires timing functions, data transfer and event monitoring in addition to sensor processing. To add comprehensive profile monitoring would greatly increase the complexity of the interrupt structure and introduce additional processing errors.
Therefore, what is desirable is a method of deriving safe separation distance for arming a missile based on calculating time to safe separation distance and making adjustments to this time based upon deviations from an acceleration profile or profiles of the missile.